Ag Bonding Wire Composition for Stable Ball Bond Reliability
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Solution Overview
Problem
Existing Ag bonding wires face challenges in high density semiconductor mounting with issues such as low bond reliability, neck damage, leaning failures, and poor ball bond stability under harsh conditions like high temperature and humidity, necessitating improved materials and manufacturing processes.
Innovation Solution
A bonding wire composed of Ag with specific additives like Be, B, P, Ca, Y, La, Ce, In, Ga, Cd, Ni, Cu, Rh, Pd, Pt, and Au, optimized through controlled atomic ratios and crystal grain sizes to enhance intermetallic compound formation, bond strength, and surface properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If Ag bonding wire is used to replace Au bonding wire for cost reduction, then material cost is reduced, but bond reliability and loop stability in high density mounting deteriorate
Solution Approach 1:
The patent uses a composite material structure with a Cu core and Pd coating layer. The Cu core provides cost advantage and electrical conductivity, while the Pd coating layer provides oxidation resistance and improved bond reliability. This composite structure resolves the contradiction between cost reduction and reliability improvement in high density mounting applications.
2Loss of substance
If Cu is used as bonding wire material to replace Au, then material cost is reduced, but oxidation resistance deteriorates
Solution Approach 1:
The patent employs a two-layer composite structure where Cu serves as the core material providing cost advantage and electrical conductivity, while Pd forms the outer coating layer providing superior oxidation resistance. This composite approach allows the bonding wire to achieve both cost reduction and maintained oxidation resistance.
Solution Approach 2:
The Pd coating layer acts as a protective thin film shell surrounding the Cu core. This flexible protective layer prevents direct exposure of the Cu core to oxidizing environments, thereby maintaining oxidation resistance while allowing the cost-effective Cu material to be utilized.
3Object-affected harmful factors
If Pd-coated Cu wire is used to improve oxidation resistance, then oxidation resistance is improved, but hardness increases after bonding
Solution Approach 1:
The patent optimizes the Pd coating thickness parameter to be between 0.01 μm and 0.05 μm. By controlling this parameter, the bonding wire achieves sufficient oxidation resistance while limiting the hardness increase that would occur with thicker Pd layers. This parameter optimization resolves the contradiction between oxidation resistance and hardness control.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides stable bond strength, prevents neck damage, reduces leaning failures, and improves ball bond reliability under high temperature and humidity conditions, ensuring a service life of 300 hours or more.
Implementation Method 1
the tip of the wire is heated to melt by arc heat input
Implementation Method 2
a ball is formed by surface tension
Implementation Method 3
this ball part is compression bonded on an electrode on a semiconductor chip heated to 150 to 300° C.
Data Source
AI summary
Bonding wire for semiconductor devices contains one or more of Be, B, P, Ca, Y, La, and Ce in a total of 0.031 at % to obtain a 0.180 at %, further contains one or more of In, Ga, and Cd in a total of 0.05 at % to 5.00 at %, and has a balance of Ag and unavoidable impurities. Due to this, it is possible to obtain a bonding wire for semiconductor devices sufficiently forming an intermetallic compound layer at a ball bond interface to secure the bond strength of the ball bond, not causing neck damage even in a low loop, having a good leaning characteristic, and having a good FAB shape.